1. Field of the Invention
The present invention relates to a developer bearing member for developing an electrostatic latent image formed on an image bearing member with one-component developer, a developing apparatus including the image bearing member, and an image forming apparatus.
2. Description of the Related Art
Various developing apparatuses are known in which one-component developer (hereinafter referred to as “toner”) is coated in thin layer on a developer bearing member, a developing bias is applied to the developer bearing member, an electrostatic latent image formed on an image bearing member is developed with the one-component developer using an electrophotographic method or the like, and the electrostatic latent image is made visible.
As the one-component developer, there are a magnetic one-component developer including magnetic particles (hereinafter referred to as “magnetic toner”) and a non-magnetic one-component developer including no magnetic particle (hereinafter referred to as “non-magnetic toner”). However, the one-component developer is not limited to a developer including only toner particles, but may be a developer including one or a plurality of auxiliary materials which can improve fluidity of the developer, limit the amount of charge of the toner, clean the surface of the image bearing member, and so forth.
In the developing method using the non-magnetic toner, a particularly clear color copy can be obtained and image fixability is improved, so that various proposals are presented. For example, a general configuration of a conventional developing apparatus using non-magnetic toner will be described. The non-magnetic toner is contained in a developer container, and is coated uniformly in thin layer on a rotating developer bearing member (hereinafter referred to as “developing sleeve”) by the developing sleeve and an elastic blade. The distance between the image bearing member and the developing sleeve is 0.02 to 0.3 mm at a developing area and an electrostatic latent image formed on the image bearing member is made visible with the non-magnetic toner at the developing area.
At this time, a pulse bias, an AC bias, or the like is applied to the developing sleeve by a developing bias power supply. In a developing apparatus using a non-magnetic toner, no magnetic particle is included in the toner, so that insulating capacity of the toner is higher than that of a magnetic one-component developer. In particular, when image development is frequently and repeatedly performed, a specific charge amount of toner increases (charge up), the developing sleeve is contaminated, and toner cohesion on the developing sleeve increases.
A developing apparatus using a magnetic toner includes a developing magnet long in the axis direction inside the developing sleeve. The magnetic toner rotates on the developing sleeve, contacts the developing sleeve, and slides on the developing sleeve, so that the magnetic toner can uniformly obtain sufficient electric charge to develop an image from the developing sleeve. However, a non-magnetic one-component toner has few opportunities to obtain electric charge by such rotation, contact, and sliding, so that it is difficult for the non-magnetic one-component toner to obtain sufficient electric charge uniformly. Therefore, a problem may arise in that the developing density is not uniform.
In addition, another problem may arise, which is a phenomenon called sleeve ghost. The sleeve ghost is unevenness of image density due to image history. When printing is performed after a continuous unprinted area (white area), only low density development is performed. On the other hand, when printing is performed after a continuous printed area (black area), high density development is performed. Therefore, unevenness of density occurs between the printing after a continuous white area and the printing after a continuous black area.
Conventionally, a sandblast process and a knurling process are performed on the developing sleeve to improve transportability.
For example, a developing apparatus discussed in Japanese Patent Application Laid-Open No. 7-13410 (Page 4, FIG. 5) includes a developer bearing member on which spirally shaped groove making concavity and convexity is formed to improve density stability.
An image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2003-208012 (Page 5, FIG. 5) uses a developing roller on which the sandblast process with a surface roughness Rz of 1.5 μm to 10 μm is performed. Alternatively, a developing roller on which knurled grooves having a diamond pattern with a depth of 5 μm to 30 μm are engraved is used to obtain a high-quality image.
An image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2007-127809 (Page 4, FIG. 1, and Page 6, FIG. 8) uses a developer bearing member including grooves having a diamond pattern. Specifically, grooves are formed so that a plurality of grooves extending in the direction slanting to the rotation thrust direction at a sharp angle intersect with a plurality of grooves extending in the direction slanting to the direction opposite to the thrust direction at a sharp angle.
A semiconductor roll discussed in Japanese Patent Application Laid-Open No. 11-73006 (Page 3, FIG. 1) and a developing apparatus using the semiconductor roll use a developing roll on which semiconductor grooves of 101 to 109 Ω·cm are formed in the circumferential direction, whereby a developing apparatus that can obtain a high quality image is provided.
However, in the surface processing of the developing roller described above, toner charge amount (toner triboelectrification) cannot be sufficiently sharpened.
Therefore, image quality desired in recent years cannot be satisfied by the prior art.